We are developing the fluorescent antibody technique for the rapid identification of group B beta hemolytic streptoxocci in human specimens. We are obtaining data on colonization of pregnant women and newborn infants, determining which site is most frequently colonized and the stability of the carrier state. We are particularly interested in semiquantitative data on maternal colonization as it relates to neonatal infection. Based on the risk factors of prematurity and prolonged rupture of maternal membranes, we have begun a controlled study of ampicillin prophylaxis of neonatal streptococcal infections in colonized women in labor with one or the other risk factors.